GeES-02.pdf Geography Of Ethiopia And The Horn - PDF

Course Title: Geography of Ethiopia and the Horn Course Code: GeES 1011 Credit hours: 3 CHAPTER-TWO THE GEOLOGY OF ETHIOPIA AND THE HORN Instructor’s Name: Ashenafi Z. (PhD Candidate) Nov, 2024  2.1. THE GEOLOGY O...

Course Title: Geography of Ethiopia and the Horn Course Code: GeES 1011 Credit hours: 3 CHAPTER-TWO THE GEOLOGY OF ETHIOPIA AND THE HORN Instructor’s Name: Ashenafi Z. (PhD Candidate) Nov, 2024  2.1. THE GEOLOGY OF ETHIOPIAAND THE HORN ❑Geology is an Earth science that studies the evolution of the earth, the materials of which it is made of, and the processes acting upon them. ❑Much of Geology is concerned with events that took place in the remote past when no one was around to witness them and with features which are far beneath the earth’s surface where no one can see them. ❑A great deal of geological understanding must, therefore, be obtained by inference, using clues from what can be seen and what can be measured. 2  …cont’d ❑There are many such clues not only the rocks and landforms which can be observed and studied at the Earth’s surface, but also those provided by indirect methods such as: A. Geophysics (studying earthquake waves) B. Geochemistry (analysis of the detailed composition of rocks) C. Geochronology (methods for finding the ages of rocks). 3  2.2. Origin of the Universe: The Big Bang Theory ❑ Universe is the totality of apace in which everything is found. According to the Big Bang theory, the universe is the result of the explosion of matter which has extremely high density &temperature. All matter in the known universe were once concentrated into a single point,cosmic egg Violent explosion occurred After explosion, the universe contained an expanding cloud of gases largely composed of nearly 73% Hydrogen and 27% Helium. Thermonuclear fusion (union) was spontaneously initiated, and stars were born due to tremendoustemperature (11million℃). The sun's first raysof thermonuclearlight blazed acrossgalaxy 4.5 Ba. The primal earth emerged &during the next 700 million years the third 4 planet began to solidify.  2.3. The Theory of Continental Drift ❑Continental drift theory was proposed by Alfred Wegener, a German meteorologist, polar explorer and visionary, who lived between 1880 and 1930 ❑Little attention was given to this idea until 1915, when Alfred Wegener published a book titled “The Origin of Continents and Oceans”. ❑BasicAssumptions of the theory: ▪ The earth’s continents were once bunched up together in to a single huge continent called Pangaea. ▪ There was also a single super ocean covering the parts of the is called panthalassa. 5  …cont’d ▪ During the Mesozoic era, about 200 million years ago, the Pangaea began to break apart into two; these are Gondwanaland and Laurasia ▪ At a later stage, the two broke farther apart into smaller continents. ▪ Gondwanaland split in to southern landmass (S/America, Africa, the Arabian Peninsula, the Indian subcontinent,Australia andAntarctica) and ▪ Laurasia split in to northern landmass (North America and Eurasia). 6  Principal observations (Evidences) of Wegener ❑Fit of the continents: ▪ The opposing coastlines of continents often fit together. An even better fit occurs if the edge of the continent shelf is used, a little offshore. ▪ Wegener was not the first person to notice the similarities between continental coastlines. Early map makers several centuries before had made the same observation. ▪ For instance, Francis Bacon as early as 1620 speculated how the opposite shorelines of South America and Africa could be fitted together. ▪ Later, in 1858, Antonio Snider published a book indicating the breakup of and drifting apart of the continents on both sides7 of theAtlantic Ocean.  …cont’d ❑Match of mountain belts, rock types: ▪ If the continents are reassembled as Pangaea, mountains in W/Africa, N/America, Greenland, and Western Europe match up. ❑Distribution of fossils: ▪ The distribution of plants and animal fossils on separate continents forms definite linked patterns if the continents are reassembled. ❑Paleoclimates: ▪ Rocks formed 200 million years ago in India, Australia, S/America, and S/Africa all exhibited evidence of continental glaciations. 8 …cont’d 9 …cont’d 10 …cont’d 11  2.4. The Geological Processes ❑Geological processes are divided into two major groups: internal and external processes. ❑The internal processes (endogenic): ▪ Example: Earth quake, volcanism, folding, faulting, orogenesis (mountain building), and epeirogenesis (sinking of the landmass). ❑The external (exogenic): ▪ Example: weathering, mass transfer, erosion and deposition. ❑The landmass of Ethiopia, as elsewhere, is the result of the combined effect of endogenic and exogenic processes. 12  2.5. The Geological Time Scale ❑Geological Time Scale is the record of earth’s history, that is divided in to 4 units (Eon, Eras, Period and Epoch) in descending order. ❑The scheme of subdivisions is based upon various aspects and events of the earth’s history, such as: ▪ the occurrence of significant geological events, ▪ the appearance or disappearance of particular life forms, and ▪ extensive changes in environmental conditions. 13  …cont’d ❑As such, the geological time categories do not usually consist of a uniform length of time. ❑The Eras are given names that indicate the kind of life that existed in them. For instance: ▪ The precambrian Era is the age of rock. ▪ the Paleozoic Era (ancient life) is the age of invertebrates. ▪ the Mesozoic Era (middle life) is the age of reptiles. ▪ Cenozoic Era (recent life) is the age of mammals. 14  2.5.1. Age Dating Techniques ❑ There are 2 techniques of knowing the age of rocks: A. Relative Dating ❑ Relative dating uses geological evidence to assign comparative ages of fossils. ❑ Hence, we can use two ways to know the relative age of a rock (which one is younger and which is older): ❑ One way is to look at any fossils the rock may contain. If any of the fossils are unique to one of the geologic time periods, then the rock was formed during that particular time period. ❑ The second way is to use the "What is on top of the older rocks?" When you find layers of rocks in a cliff or hillside, 15 younger rocks are on top of older rocks.  B. Absolute Dating (Radiometric Techniques) ❑There are 2 majorAbsolute Dating Techniques: A. Carbon-14 Technique, and B. Potassium-40 Technique I. Carbon-14 Technique ❑Upon the organism’s death, carbon-14 begins to disintegrate at a known rate, and no further replacement of carbon from atmospheric carbon dioxide can take place. ❑Carbon-14 has half-life of 5730 years. 16  …cont’d B. Potassium-40 Technique ❑The decay is widely used for dating rocks. ❑Geologists are able to date entire rock samples in this way, because potassium-40 is abundant in micas, feldspars, and hornblendes. ❑Leakage of Argon is a problem if the rock has been exposed to temperatures above 125°C (257°F), because the age of the rock will then reflect the last episode of heating rather than the time of original rock formation. 17  …cont’d ❑NOTE: ✓Half-life is the duration of time needed for unstable element to be reduced by one–half of its original quantity to decay to atoms of anew more stable daughter element. ✓Half-life is commonly used in nuclear physics and chemistry sciences. ✓Every radioactive element has its own half- 𝒕𝟏 life, symbolized as: 18 𝟐 Half-life of Some Radioactive Elements 19  2.6. Geological Processes and the Resulting Landforms of Ethiopia and the Horn 2.6.1. The Precambrian Era(4.5 b- 600 m years ago) ❑ The 1st oldest & longest Era, covers 5/6th of the Earth’s history. Due to its remoteness in time and the absence of well-preserved fossils, our knowledge of the events is limited. ❑ The major geologic event of the Precambrian Era was: A. The first forms of life emerged (amoeba and jellyfish) B. The formation of crystalline basement rocks C. Orogenesis (the process of mountain building), D. Metamorphism (formation of metallic minerals), and E. Intensive volcanic activities. ❑ The Precambrian rocks are overlaid by recent rock formations. However, as surface rocks covering 25% of the land mass of the 20 country, exposed in the N, S, E and W parts of Ethiopia.  2.6.2. The Paleozoic Era (600-225 m years ago) ❑ The 2nd longest and 2nd oldest era, marked by the presence of first organism. ❑ The major geological processes of this Era was: A. Denudation and peneplanation B. Heavy erosion, and C. Formation of coal ❑ The gigantic mountains that were formed by the Precambrian orogeny were subjected to intense and prolonged denudation. ❑ At the end, the once gigantic mountain ranges were reduced to a “peneplained” surface. ❑ Due to limited deposition in Ethiopia there is no significant 21 rock formation in Paleozoic era.  2.6.3. The Mesozoic Era(225-70 m years ago) ❑The 3rd largest and 3rd oldest era. It was an Era of alternate sinking and rising (epeirogenesis) of the landmass. ❑The major geological processes were: ▪ Movement of continents ▪ Sinking and uplifting of the landmass. ▪ Formation of the 3 layers of marine sediments. ▪ Appearance and disappearance of dinosaurs. ▪ Emergence of mammals, birds & flowering plants. 22  …cont’d ❑ The landmass sank during the Mesozoic’s Triassic and Jurassic periods: ▪ In the Triassic Period, the landmass sank due to internal forces. This event was followed by transgression of a nearby sea into the mainland of today’s Somalia, and south-eastern Ethiopia, the oldest sedimentary rock (Adigrat sandstone )was formed. ▪ In the Jurassic Period, the transgression of the sea continued into the mainland in the northwest direction. This event deposited another sedimentary rock (Hintalo limestone). ▪ In the Cretaceous Period, the landmass began to rise and the sea started to regress towards the southeast, depositing sedimentary rock (Upper Sandstone). Upper Sandstone is the youngest 23 sedimentary rock, and therefore overlies the rest.  2.6.4. The Cenozoic Era (70m years ago - Present) ❑The most recent and shortest Era. ❑The 3 major geologic activities were: 1. Uplifting of the Arabo-Ethiopian landmass and outpouring of huge quantity of lava. 2. Formation of the Rift Valley. 3. Quaternary volcanism & deposition. 24  1. Uplifting of the Arabo-Ethiopian landmass and outpouring of lava flood ❑The uplifting of the whole of the Arabo-Ethiopian landmass is a continuation of the slow rise that began in the Upper Jurassic and Cretaceous periods. ❑This huge uplift continued to the Paleocene and Oligocene epoch of the Tertiary period. ❑During the Eocene epoch, the uplifting was of greater magnitude, the land was pushed up to a 25 maximum height of 2,000 masl.  …cont’d ❑The greatest uplift was in central Ethiopia. This immense tectonic force also fractured the crust at many places. ❑Accordingly, Huge quantity of lava came out through these fractures. ❑The mass of lava was so immense, that it formed a thick layer of volcanic rocks on the plateau, which mounted to more than 1,000 masl in the north Central Highlands. ❑Where the lava comes out through vents, huge volcanic rocks were piled up and form huge Volcanic Mountains’, known as Trappean lava or Trap Series lava. 26  2. The Formation of the Rift Valley ❑The formation of the Rift Valley is said to be related with the theory of plate tectonics. ❑According to the theory, the Rift Valley may be lying on the Earth’s crust below which lateral movement of the crust in opposite directions producing tensional forces that caused parallel fractures or faults on the sides of the up-arched swell. ❑As the tension widened the fractures, the central part of the landmass collapsed to form an extensive structural depression known as the Rift Valley. 27  …cont’d ❑The major faulting movement began in the late Oligocene and Miocene Epochs of Cenozoic Era. ❑This rifted the Red Sea trough, which began to be flooded from the north. ❑But the major rifting, affecting the whole African Rift System, including that of Ethiopia and the Gulf of Aden took place in the Miocene Epoch. ❑Rifting and faulting, however, continued all the time throughout the Pliocene and even the Pleistocene Epochs. 28  …cont’d ❑ The Red Sea & Gulf of Aden were connected as a result of the rifting and faulting of the land bridge that separated them. ❑ At the same period (Pliocene), the Afar depression (including the Gulf of Zula) was down-faulted allowing the Red Sea water to penetrate far inside. ❑ Reversed tilting and volcanic activity, later (Pleistocene) blocked the connection and isolated the extension of the sea, allowing much of the water to evaporate. As a result, thick saline materials accumulated. ❑ During the same period, the area between the Danakil Depression and the Red Sea was uplifted to form the Afar 29 Block Mountains.  The Spatial Extent of the Rift Valley ❑The Ethiopian Rift Valley is part of the Great East African Rift valley. ❑The Great East African Rift valley is the largest rift valley in the world, that extends from Palestine-Jordan in the north to Malawi-Mozambique in the south, for a distance of about 7200 kms. ❑Of these, 5600 kms is in Africa, and 1700 kms in Eritrea and Ethiopia. ❑The widest part of the Rift Valley is the Afar Triangle (200-300 km). 30  …cont’d ❑The Red Sea, Gulf of Aden, and East African Rift System meet and form the triangular depression of the Afar where the Kobar Sink lies about 125 mbsl. ❑The Rift Valley region of Ethiopian is the most unstable part of the country. ❑There are numerous hot springs, fumaroles, active volcanoes, geysers, and frequent earthquakes. 31  …cont’d ❑The formation of the Rift Valley has the following structural effects: ▪ It divides the Ethiopian Plateau into two. ▪ It separates the Arabian landmass from African landmass. ▪ It causes the formation of the Dead Sea, Red Sea and Gulf of Aden. ▪ It creates basins and fault depressions on which the Rift Valley lakes are formed. 32  3. Quaternary Volcanic Eruptions and Depositions ❑They are recent volcanic activities that took place after the formation of the Rift Valley. This occurred in the Pliocene-Pleistocene Epochs. ❑This activity was generally limited to the floor of the Rift Valley and the region south of Lake Tana, where the lava covers an area of more than 𝟑𝟎𝟎𝟎𝐤𝐦𝟐. ❑However, Aden volcanics and recent faulting are more extensively developed in theAfar region. ❑Because of their recent occurrence, the Aden volcanic have relatively well-preserved and visible morphological 33 features.  …cont’d ❑The basic volcanic features of the Aden series include: ▪ Numerous & freshly preserved volcanic cones ▪ Volcanic hills and mountains ▪ Extensive lava fields and lava sheets ▪ Lava ridges, and ▪ Thermal springs, fumaroles. 34  Quaternary Deposition ❑ During the Quaternary period of the Cenozoic Era, the Earth experienced a marked climatic change, warmer and dry periods were alternating with cooler and wet periods. ❑ This was the time of the last ‘’Ice Age’’ in the middle and high latitude areas and the time of the ‘‘Pluvial Rains’’inAfrica. ❑ The major effects of the excessive pluvial rain were: Excessive surface flow, Rivers were many and large, Eroded the Ethiopian plateau, Rivers carried a lot of water and sediments. Lake and marshy areas became numerous and deep. Many lakes were merged together. 35  …cont’d ❑ For example, Ziway-Langano-Shalla; Hawasa-Shallo; Chamo-Abaya; and Lake Abe and the nearby smaller lakes and marsh basins formed huge lakes. ❑ After the ‘‘Pluvial Rains’’, the Earth’s climate became warmer and drier. ❑ Thus, it increased the rate of evaporation that diminished the sizes of the lakes. ❑ Today, there are lacustrine deposits of continental origin around many of the Ethiopian lakes, river valleys & lowlands. ❑ The quaternary deposits are mainly found in the RV(Afar and Lakes Region), Baro lowlands, southern Borena, & parts of 36 NW low lands.  …cont’d ❑ According to the place and manner of deposition and depositing agents these deposits are divided as follow. I. Lacustrine: Deposits on former lakebeds and swampy depressions. II. Fluvial: Deposits on river banks, flood plains, plateau and foothills. III. Glacio-fluvial: Deposits on high mountains (Bale and Kaka). IV. Aeolian deposits:Are windblown deposits. V. Coastal & marine: Deposited on sea invaded and sea-covered places. ❑ Generally, cenozoic rocks cover 50% of the land mass of the country. These include Highland Tertiary volcanics (basalts), Tertiary as well 37 as Quaternary volcanics, and sediments of the rift valley.  2.7. Rock and Mineral Resources of Ethiopia ❑Rocks are a naturally formed solid aggregate of one or more minerals. ❑According to Geologists, mineral is naturally occurring, inorganic, solid element or compound with a definite chemical composition which can be represented by a chemical formula and regular/specific internal structure. ❑The occurrence of metallic minerals in Ethiopia is associated with the Precambrian rocks. ❑Although not in sufficient concentration and extent, a great variety of such minerals occur in the basement rocks. 38  …cont’d ❑ Conditions that must be satisfied for a substance to be a mineral are: ✓ It must occur naturally as an inorganic substance, i.e. it is not manufactured by man or it is not synthetic. ✓ It must be a crystalline solid, i.e. it must have an orderly internal structure. Minerals are crystalline at least on the microscopic scale. Liquids or gases cannot be minerals. The only exception is mercury. For example, ice of glacier is a mineral but liquid water is not. ✓ It must have a definite chemical composition. Its composition must be such that it can be represented by a definite chemical 39 formula.  2.7.1. Brief Facts and Current State of Main Minerals in Ethiopia ❑Geological surveys proved that Ethiopia has abundant mineral resources of metals and precious metals, coal, and industrial minerals. ❑Gold, Platinum, Tantalum, Gemstones, Potash, Gypsum andAnhydrite, Clay, Marble, Construction stones…etc. ❑However, there is a huge gap between the mineral potential of the country and actual level of utilization. ❑This is mainly because of lack of technology, capital and skilled manpower. 40  2.7.2. Mineral Potential Sites of Ethiopia ❑According to the Ethiopian geological survey, the geologic formations that host most mineral potentials of Ethiopia includes three major greenstone belts and other formations. ❑These are: I. The Western and South-western-greenstone belt II. The Southern greenstone belt III. The Northern greenstone belt 41  I. The Western and SW-greenstone belt ❑They contain various minerals: ▪ primary gold occurrences (Dul,Tulu Kape,Oda- Godere,Akobo,Baruda,Bekuji-Motish and Kalaj); ▪ Yubdo Platinum, ▪ Base metals ofAzaliAkendeyu,Abetselo and Kata; ▪ Fakushu Molybdenite and the iron deposits of Bikilal, Chago, Gordana and Korre, ▪ Benshagul Gumuz Marble, and ▪ Akobo andAsosa placer gold deposits. 42  II. The Southern greenstone belt ❑It is known as the Adola belt, which comprises: ▪ The primary gold deposits and occurrences of Lega- dembi, Sakaro, Wellena, Kumudu, Megado-Serdo, Dawa Digati, Moyale andAbaba River; ▪ The columbo-tantalite of kenticha and Meleka, and ▪ The Adola nickel deposit and other industrial minerals. 43  III. The Northern greenstone belt ❑This belt comprises: ▪ The primary gold occurrences of Terakemti, Adi-Zeresenay, and Nirague. ▪ The base metals of Terer, Tsehafiemba and other parts of Tigray, and ▪ Placer gold occurrences of Tigray. 44 45